import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class UdpEchoServer {
    private DatagramSocket socket = null;

    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }

    public void start() throws IOException {
        System.out.println("服务器启动！");
        //通过一个死循环来不停地处理请求
        while(true) {
            //1. 读取客户端的请求并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096],4096);
            socket.receive(requestPacket);
            //将收到的二进制 byte[] 数据转换成字符串
            String request = new String(requestPacket.getData(),0,requestPacket.getLength());
            //2. 根据请求计算响应
            String response = process(request);
            //3. 把响应写回到客户端
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(),response.getBytes().length,
                    requestPacket.getSocketAddress());
            socket.send(responsePacket);
            //4. 打印日志
            System.out.printf("[%s:%d req=%s, res=%s\n",requestPacket.getAddress(),requestPacket.getPort(),request,response);
        }
    }

    //请求是什么，响应就是什么
    private String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }
}
